How to add a custom panel to particle properties?
You need to register the class to use it. 

Also bl_context = "PARTICLES" should be replaced by bl_context = "particle"

Here's the complete script

import bpy


class CudaParticlePanel(bpy.types.Panel):
    bl_idname = "CudaParticle_Panel"
    bl_label = "CudaParticle"
    bl_category = "SYSTEM"
    bl_space_type = 'PROPERTIES'
    bl_region_type = 'WINDOW'
    bl_context = "particle"

    def draw(self, context):    
        layout = self.layout
        layout.label(text= "CudaParticals Properties:")
        self.layout.label(text="CudaParticle")


def register():
    bpy.utils.register_class(CudaParticlePanel)


def unregister():
    bpy.utils.unregister_class(CudaParticlePanel)


if __name__ == "__main__":
    register()